Chitin, the main component of the exoskeletons of arthropods, the pen of squid, the cell walls of fungi, and the like, is the second most abundant natural biopolymer in the world and is widely used in various application fields, such as agriculture, food/nutrition, medicine and biomedical engineering, material science, nanotechnology, cosmetics, wastewater treatment, paper production, textile industries, and the like.
Chitin molecule is a long-chain biopolymer which is composed of β-1,4-linked N-acetyl-D-glucosamine units. In the exoskeletons of arthropods, the pen of squid, and the cell walls of fungi, chitin molecules are grouped into tight bundles to form highly crystalline chitin nanofibers, wherein the structure of the chitin nanofiber is stabilized by hydrogen bonds and van der Waals forces. Many chitin nanofibers are interact with each other and proteins to form aggregated thicker and tight bundles, that is, the chitin microfibrils. Finally, many chitin microfibrils are interact with minerals and/or proteins and then aggregate a much bigger structure to form said exoskeletons of arthropods, said pen of squid, or said cell walls of fungi.
Generally, all of the commercial chitin products are composed of the exoskeletons of arthropods (or the pen of squid, the cell walls of fungi) in granule, powder, or piece form, wherein the exoskeletons (or pen, cell walls) are obtained through the steps of purifying the exoskeletons of arthropods (or the pen of squid, the cell walls of fungi) and removing the proteins and minerals in the purified exoskeletons (or squid pen, cell walls). Chitin in the present invention is the exoskeletons of arthropods, the pen of squid, the cell walls of fungi, or the like prepared by the same steps as these commercial chitin products.
Chitin is a good source of biological nanofiber. To obtain chitin nanofibers, destroying two forces in chitin microfibrils is required: (1) the force between chitin nanofibers; and (2) the force between chitin nanofiber and proteins/minerals.
Chitin is classified into three different crystalline forms: the Alpha-, Beta-, and Gamma-form, different in the arrangement of chitin molecule chains within chitin nanofibers. Alpha chitins (α-chitins) are composed of antiparallel chains and are found in the exoskeletons of insects. Beta chitins (β-chitins) are composed of parallel chains, often found in squid. Gamma chitins (γ-chitin) are composed of 2 parallel chains alternating with an antiparallel chain and are found in fungi.
At present, the methods for preparing chitin nanofiber includes a grinding method, an ultrasonic method, an electrospinning method, and an acid hydrolysis method. However, these methods are hard to be used in large scale production, take long time, use complex process, and thus have their limitation in application. Therefore, an easy and effective method for preparing a large number of chitin nanofibers is required.